Step used in the difference
approximation to the Jacobian. If
optDelta<0, the Jacobian is approximated
with central differences which are more
accurate (but slower!) compared to the
forward differences employed by default.

Cannot solve a problem with fewer
measurements than unknowns. In case
linear constraints are provided, this
error is also returned when the number
of measurements is smaller than the
number of unknowns minus the number of
equality constraints.